test_strings: Remove string tests that exercise asserts.

test_strings:  Remove string tests that exercise asserts.

Since unit tests are run with DO_CRASH, those tests were causing
the test to fail.

Tested-by: George Joseph
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Merged revisions 427354 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 427355 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 427356 from http://svn.asterisk.org/svn/asterisk/branches/13

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@427357 65c4cc65-6c06-0410-ace0-fbb531ad65f3